# OpenFOAM-CalculiX FSI Diverging Sim Never Ends

**URL:** <https://precice.discourse.group/t/openfoam-calculix-fsi-diverging-sim-never-ends/645>\
**Category:** Using preCICE\
**Tags:** openfoam, calculix, fsi\
**Created:** [June 30, 2021, 4:37pm UTC](https://precice.discourse.group/t/openfoam-calculix-fsi-diverging-sim-never-ends/645 "2021-06-30T16:37:40Z")\
**Posts on this page:** 1\
**Showing post:** 14

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**Author:** ![uekerman](https://yyz2.discourse-cdn.com/free1/user_avatar/precice.discourse.group/uekerman/32/2199_2.png) [@uekerman](https://precice.discourse.group/u/uekerman)\
**Post date:** [July 25, 2021, 3:15pm UTC](https://precice.discourse.group/t/openfoam-calculix-fsi-diverging-sim-never-ends/645/14 "2021-07-25T15:15:21Z")

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Do you start from a rather converged (single-physics) fluid simulation?  
I would always recommend this for such strongly-coupled problems.  
Once Aitken converges, you should switch to IQN. Aitken could get terribly slow here.  
Also be aware that small timestep sizes can lead to more stability problems for FSI with an incompressible fluid.

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